Water Spinner

When
a thin, flat, vertical tank of water spins around on a turntable,
the water surface forms a parabola. The visitor turns a crank
which makes the turntable rotate, and thus controls the speed
of rotation. When the tank rotates rapidly the surface forms a
deeply curved parabola; when it rotates slowly it forms a shallow
parabola. The visitor can also use a magnet to position several
rods, which float vertically when the water is at rest. When the
tank rotates however, these rods align themselves perpendicular
to the surfacethey are no longer vertical.
The surface of the water is perpendicular to the net force in
the rotating frame of reference.